1. Field of the Invention
The present invention relates to a photographic element for a color diffusion transfer process (DTR color) and, particularly, to a photographic element having a novel timing layer for neutralization formed from a polymer latex.
2. Description of the Prior Art
Heretofore, a neutralizing layer has been used in the color diffusion transfer process to decrease the pH in a photosensitive layer and to thereby interrupt the formation of a color image (development). Further, in a photographic element for the color diffusion transfer process, a timing layer which controls the period of time at a high pH at which the photographic element is processed based on the temperature has been provided in association with a neutralizing layer as described in W. T. Hanson Jr., Photographic Sci. & Eng., Vol. 20, p. 155 (1976).
It is advantageous in a color diffusion transfer process which uses a dye image providing material which is not diffusible initially but releases a diffusible dye as a result of an oxidation-reduction reaction or a coupling reaction with an oxidation product of the developing agent as described, for example, in Japanese Patent Application (OPI) No. 33826/73 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application"), U.S. Pat. Nos. 3,929,760, 3,931,144 and 3,932,381, to provide a timing layer which has a "temperature-compensating" function. That is, where the development of silver halide is slow and the above-described oxidation-reduction reaction is delayed, deterioration of densities of transferred color images results from the delay in the diffusion of dyes at a low temperature. This can be corrected by prolonging the period of time at which development occurs under a high pH (namely, prolonging the period of time where developing of silver halide and release and transfer of the dyes can occur) using a timing layer having a "temperature-compensating" function, wherein the water permeability of the layer at low temperatures decreases a fixed image density is obtained regardless of variation in the processing temperature.
Examples of timing layers having a "temperature-compensating" function include timing layers composed of polyvinyl alcohol as described in U.S. Pat. No. 3,362,819, layers described in Japanese Patent Application (OPI) No. 22935/74 (corresponding to U.S. Pat. No. 3,785,815) and layers described in Research Disclosure, p. 86, November 1976, e.g., timing layers formed from a latex of methyl acrylatevinylidene chloride-itaconic acid copolymers or acrylonitrilevinylidene chloride-acrylic acid copolymers).
However, in the timing layers described in U.S. Pat. No. 3,785,815, the delay in development cannot be adequately compensated for, because the degree of the decrease of the permeability in the timing layer at the low temperature range is small. Further, in the timing layers described in Research Disclosure, supra, there is the defect that the cost of production is high, because it is necessary to use vinylidene chloride which requires special equipment for producing the polymer latex since it is hazardous to humans and has a low boiling point.
Furthermore, when a cover sheet including a neutralizing system and a photosensitive sheet comprising an image-receiving element and a photosensitive element coated in turn on a support are combined to form a laminate integral type film unit using a heat seal treatment which is suitable for a high speed mass-production and the film unit is handled somewhat roughly, in particular, at a low temperature, the heat sealed portion of the film unit is liable to be broken and the processing solution is liable to spread between the photosensitive sheet and the cover sheet and leak out of the film unit. In most cases the peeling of the film unit which results in the above-described instance is due to poor adhesion between the timing layer and the layers adjacent thereto. Thus, a timing layer exhibiting good adhesion to the layers adjacent it such that peeling does not occur during manufacture would be desirable.